The present invention relates to a phase locked loop (PLL) circuit that receives a first reference signal, which is generated by superimposing a wobble signal on a land pre-pit signal, and a second reference signal, which is generated from a wobble signal, to generate a clock signal synchronized with either one of the first reference signal and the second reference signal.
Recently, various types of disc-type recording media, such as optical discs are becoming more popular. Disc recording media, such as for example, a Digital Versatile Disc-Recordable (DVD-R), a Digital Versatile Disc-Rewritable (DVD-RW), a Digital Versatile Disc + Recordable (DVD+R), and a Digital Versatile Disc + ReWritable (DVD+RW) have been introduced to the market. Although the format of the data recorded on the disc recording medium is the same in these disc recording media, the recording format of the disc positional information in DVD-R and DVD-RW media differs from that in DVD+R and DVD+RW media. The DVD-R and the DVD-RW (hereinafter referred to as DVD-R/RW) and the DVD+R and the DVD+RW (hereinafter referred to as DVD+R/RW) are standardized disc recording media for recording data in compliance with the same data format, as shown in FIG. 13.
FIG. 13 shows the configuration of one sector of the recording data in a DVD. The DVD data to be recorded on the DVD disc medium consists of 32 bits of synchronizing signal (SYNC in FIG. 13) and 1456 bits of modulated data. In other words, 728 bits of data are 8-16 modulated to produce 1456 bits of data, and 32 bits of a synchronizing signal (SYNC) are added to the head of each of the 1456 bits of modulated data. This generates one frame of recording data. In a DVD, 26 frames of recording data make up one sector.
The recording format of disc positional information recorded on the DVD disc medium differs depending on the type of the DVD disc medium.
The DVD-R/RW is provided with a track formed by a groove, which is formed in a flat surface (land) of the disc. The groove is formed so as to meander at a rate of sixteen cycles for every two frames in a data recording region in the format data (FIG. 14(a)). A wobble signal having a predetermined cycle is extracted from such meandering (wobble) of the groove.
Further, the DVD-R/RW has, in addition to the wobble, a Land Pre-Pit (LPP), which represents disc positional information on the track and which is provided at predetermined intervals. The LPP is provided for every two frames in the data recording region in the above format data. A group of the LPPs that are provided for each of sixteen sectors of the recording region in the above format data represents positional information of the disc.
The DVD+R/RW is also provided with a track formed by a groove, which is formed in a flat surface (land) of the disc. A wobble signal having a predetermined cycle is extracted from the meandering (wobble) of the groove. The meandering cycle of the DVD+R/RW groove is longer than the meandering cycle of the OVD-R/RW groove. The DVD+R/RW groove meanders at a rate of 93 cycles for every two frames in a data recording region in the above format data.
There are no LPPs formed on the DVD+R/RW. In place of the LPP, the groove is formed so that phase-modulation is performed on the wobble signal of the predetermined cycle in accordance with disc positional information, which is referred to as Address In Pregroove (ADIP). More specifically, the wobble is phase-modulated once for every two frames in the data recording region in the above format data. The ADIPs acquired from each of four sectors of the recording region in the above format data represent the disc positional information.
The recording of data to a disc medium is performed by irradiating a laser beam on the disc medium, the rotation of which is controlled. It is preferred that the recording of data be performed in accordance with a reference clock signal, which corresponds to the rotation of the disc medium. The reference clock signal enables the recording region for every one bit of data that is recorded to the disc medium to be constant and thus enables the recording of data to be accurately controlled.
A PLL circuit uses a reproduced wobble signal or LPP signal to generate a pulse signal, which is synchronized with the wobble signal and the LPP signal, to acquire the reference clock signal. Japanese Laid-Open Patent Publication No. 2002-230915 describes a conventional PLL circuit. The PLL circuit compares the phase of a clock signal, the oscillation of which is controlled by a voltage-controlled oscillator, and the phase of a wobble signal or LPP signal to calculate a frequency difference between the two signals. Then, the PLL circuit feeds back voltage, which is in accordance with the frequency difference, to the voltage-controlled oscillator. This synchronizes the clock signal with the wobble signal or the LPP signal.
The recording format of the disc position information differs between the DVD-R/RW media and the DVD+R/RW media. Thus, a data recording controller that may be used in a compatible manner for both DVD-R/RW and DVD+R/RW includes a DVD-R/RW clock signal generation circuit and a DVD+R/RW clock signal generation circuit. The circuit scale (size and number of devices) of a clock signal generation circuit is relatively large. This enlarges the circuit scale of a data recording controller provided with both DVD-R/RW and DVD+R/RW clock signal generation circuits.